MOST CD56(-) T-CELL LYMPHOMAS OF MONOMORPHIC SMALL TO MEDIUM-SIZE HISTOLOGY() INTESTINAL LYMPHOMAS ARE CD8(+)CD5()

The expression of the natural killer (NK) cell marker CD56 has been re ported to occur in NK cell lymphomas/leukemias and a small group of pe ripheral T-cell lymphomas but has not been studied extensively in prim ary intestinal non-B-cell lymphomas. Normal human jejunal intraepithel ial lymphocytes (IELs) are mainly T-cell receptor (TCR)-alpha beta(+)C D3(+)CD8(+)CD5(low) and include an similar to 15% fraction of CD56(+) cells that could be the cells of origin for CD56(+) intestinal T-cell lymphoma (ITL). To test this hypothesis, 70 cases diagnosed as ITL wer e immunophenotyped, and 15 CD56(+) cases (21%) were identified. The ma jority of the CD56(+) lymphomas was of monomorphic small to medium-siz ed histology, shared the common phenotype beta F1(+/-)CD3 epsilon/cyt( +)CD8(+)CD4(-)CD5(-)CD57(-)TIA-1(+) and had clonally rearranged TCR ga mma-chain genes. In contrast, the CD56(-) lymphomas were mainly compos ed of pleomorphic medium and large cells or had a morphology most cons istent with anaplastic large-cell lymphoma and were mostly CD8(-). The se findings suggest that the majority of CD56(+) intestinal lymphomas are morphologically and phenotypically distinct T-cell lymphomas most likely derived from activated cytotoxic CD56(+)CD8(+) IELs. Some overl apping histological and clinical features between CD56(+) and CD56(-) ITLs indicate that the former belong to the clinicopathological entity of ITL, The consistent expression of cytotoxic-granule-associated pro teins introduces ITL (both CD56+ and CD56-) into the growing family of usually aggressive extranodal lymphomas of cytotoxic T-cell and NK-ce ll derivation. In contrast to putative NK-cell lymphoma of the sinonas al region, intestinal NK-cell lymphoma seems to be very rare.